1. Field of the Invention
This invention relates to a touch signal probe used to measure the shape of a measured object, etc., with a three-dimensional measuring machine, etc.
2. Description of the Related Art
A three-dimensional measuring machine, etc., is known as a measuring machine for measuring the shape, the dimensions, etc., of a measured object. To detect the coordinates and the position of the measured object, the measuring machine uses a touch signal probe comprising a contact ball at the tip part of a stylus to detect the contact ball coming in contact with the measured object.
A related art example of the touch signal probe is shown in Japanese Patent Unexamined Publication No. Hei. 10-288502.
In the related art example, four piezoelectric elements 121 to 124 are attached to a stylus 101, as shown in FIG. 11A. The stylus 101 comprises a rod 101B to which a contact ball 101A is attached at a tip part, and a detection element support part 101C formed integrally with a base end part of the rod 101B. The detection element support part 101C is formed at both ends with flange parts 101D each being square in cross section. The piezoelectric elements 121 to 124 are fixedly secured to the sides of the flange parts 101D. Each of the piezoelectric elements 121 to 124 is shaped like a flat rectangle parallel with an axis of the stylus in the length direction of the piezoelectric element, as shown in FIG. 11B.
In the related art example, when the contact ball 101A comes in contact with a measured object, the impact force at the contact time is detected at the piezoelectric elements 121 to 124. Contact sense signals are generated based on the sum, the difference, and the square sum of signals output from the piezoelectric elements 121 to 124, and are processed. Thus measurement with high accuracy can be conducted with directional dependence eliminated.
In the related art example, each of the piezoelectric elements 121 to 124 is placed in parallel with the axis of the stylus in the length direction of the piezoelectric element. Thus, in response to the action of the external force produced by the contact in a direction P which causes the rod 101B to bend, a force of expanding or contracting along the length direction of the piezoelectric element occurs, and the sensitivity becomes extremely good. However, the sensitivity is not necessarily sufficient depending on the direction of the external force acting on the rod 101B.
In an actual probe, the rod 101B may be provided with a plurality of contact balls 101A1 to 101A4 radially extending, as shown in FIG. 12. In the actual measurement operation with the probe shown in FIG. 12, if an external force acts on any of the contact balls 101A1 to 101A4 and a measured force in a torsion direction indicated by an arrow Q is given to stylus main body 101B, the force of expanding or contracting along the length direction of each of the piezoelectric elements 121 to 124 does not work. Thus, the sensitivity of the piezoelectric elements 121 to 124 is degraded and change in the state quantity cannot sufficiently be detected.
Thus, in the related art example, a disadvantage that a touch signal is not generated although the contact ball is in contact with the measured object occurs.
Generally, a three-dimensional measuring machine on which a touch signal probe is mounted stops the measurement operation and performs avoidance operation based on a touch signal. Thus, if a measured force in the torsion direction Q occurs in the probe shown in FIG. 12, the measurement operation cannot be stopped and it is feared that both the measured object and the three-dimensional measuring machine may be broken.
It is an object of the invention to provide a touch signal probe capable of detecting with high sensitivity not only a measured force in a bend direction of a stylus, but also measured force in a torsion direction.
Thus, the invention is intended for accomplishing the object by attaching a displacement detection element in a state in which the displacement detection element is inclined at a predetermined angle relative to an axis of a stylus to detect both the measured force in the bend direction of the stylus and the measured force in the torsion direction.
Specifically, according to the invention, there is provided a touch signal probe comprising: a stylus having as contact ball for coming in contact with a measured object at a tip; and a displacement detection element attached to the stylus for detecting the contact ball coming in contact with the measured object. In the touch signal probe, the stylus has a detection element support part for supporting and fixing the displacement detection element and a rod placed on the detection element support part. The detection element support part has a plurality of flange parts each being regular polygonal in cross section orthogonal to an axis of the rod. The displacement detection element is attached to sides of the flange parts in a state in which it is inclined at a predetermined angle xcex1 (0xc2x0 less than xcex1 less than 90xc2x0) relative to the axis of the rod. Then a contact sense signal is generated based on a signal output from the displacement detection element.
In the invention, the displacement detection element is attached to the sides of the flange parts in a state in which it is inclined at the predetermined angle relative to the axis of the rod, so that if a measured force in the torsion direction occurs on the rod through the contact ball, the measured force is transmitted along substantially the length direction of the displacement detection element.
Thus, the displacement detection element is reliably expanded or contracted and is enhanced in sensitivity and can detect change in the state quantity sufficiently.
In contrast, if a measured force in the bend direction occurs on the rod through the contact ball, the measured force is transmitted along substantially the length direction of the displacement detection element.
Thus, the displacement detection element is reliably expanded or contracted and is enhanced in sensitivity and can detect change in the state quantity sufficiently.
That is, if the contact ball comes in contact with a measured object from any direction, a touch signal is reliably generated because the displacement detection element has high sensitivity. Further, the displacement detection element is attached to the sides of the polygonal bodies, so that the structure of the touch signal probe can be simplified.
In the invention, preferably the cross section of each of the flange parts orthogonal to the axis of the rod is made square and a total of four displacement detection elements are attached to the sides of the flange parts so that the displacement detection elements are spaced 90 degrees from each other.
In this configuration, a touch sense signal is generated based on the signals output from the four displacement detection elements spaced 90 degrees from each other with the stylus axis as the center, so that measurement with good accuracy can be conducted. Moreover, the cross section of each flag part is made square, so that the structure of the touch signal probe can be simplified.
The displacement detection elements may be mounted on the detection element support part so that the displacement detection elements opposed to each other become substantially mirror-symmetrical.
In this configuration, if a measured force in the torsion direction occurs on the stylus, positive and negative output signals are generated on a pair of displacement detection elements placed facing each other with the flange parts between. Thus, the difference between the signals is obtained for each of the two pairs of displacement detection elements, and the difference signals are squared and are added. Thus a large detection signal can be provided and the measurement accuracy can be improved.
Further, the displacement detection elements may be mounted on the detection element support part so that the displacement detection elements opposed to each other become symmetrical with respect to the axis of the stylus.
In this configuration, if a measured force in the torsion direction occurs on the stylus, the same positive or negative output signal is generated on all the four displacement detection elements. Thus, the signals are added, whereby a contact signal can be provided easily.